This application includes the following proposals: 1) double blind controlled treatment trial of ursodeoxycholic acid, (2) study of effects of udc treatment on composition of biliary lipids (lithogenic index) and bile acid kinetics, (3) study of the pathway and site of the interconversion between chenodeoxycholic acid and ursodeoxycholic acid using labeled cdc, udc, and 7-keto lithocholic acid, (4) study of the role of intestinal bacteria in the interconversion between cdc and udc using the cholyl-glycine-1-14C breath test and in vitro techniques, (5) study of the relationship between bile acid deconjugation and changes in biliary lipid and bile acid composition in ileitis, (6) study of the incidence and site of bile acid deconjugation in ileitis using the cholyl-glycine-1-14C breath test and the measurement of fecal excretion of bile acid label.